System for transmitting and receiving short message service (SMS) messages

ABSTRACT

A system for accessing broadcast SMS messages over a wireless communication system. A base station transmits SMS messages periodically and aperiodically over a broadcast channel. The base station allocates periodic slots in the broadcast channel for each of the subscriber services providing the SMS messages and transmits slot parameters to mobile units. Using the slot parameter information, the mobile units periodically wake up to scan the broadcast channel. The period for each category of broadcast SMS messages may be different and the period may apply to a single broadcast channel. Messages arriving aperiodically can be queued and transmitted in pre-scheduled broadcast channel frames. Messages with inter-arrival interval greater than the specified transmission period are simply repeated.

BACKGROUND OF THE INVENTION

[0001] I. Field of the Invention

[0002] The present invention pertains generally to the field ofcommunications, and more particularly to the broadcast of short messageservice for wireless communication systems.

[0003] II. Background

[0004] In a wireless communication system, the broadcast short messageservice (SMS) allows the transmission of short messages from asubscription service to a mobile unit. Generally, broadcast SMS messagesare messages associated with services subscribed to by a user. BroadcastSMS can comprise entry features, administration features, or informationmessages. For example, a subscriber may subscribe to a stock quotesservice wherein the subscriber will receive stock quotes on a wirelessdevice or a mobile unit, such as a personal data assistant (PDA), laptopcomputer, a cellular telephone or a PCS telephone, from a subscriptionservice utilizing the wireless communication system.

[0005] Various over-the-air interfaces have been developed for wirelesscommunication systems including, e.g., frequency division multipleaccess (FDMA), time division multiple access (TDMA), and code divisionmultiple access (CDMA). In connection therewith, various domestic andinternational standards have been established including, e.g., AdvancedMobile Phone Service (AMPS), Global System for Mobile Communications(GSM), and Interim Standard 95 (IS-95).

[0006] An exemplary wireless telephony communication system is a codedivision multiple access (CDMA) system. The IS-95 standard and itsderivatives, IS-95A, IS-95B, IS-2000, proposed high-data-rate CDMAstandards exclusively for data, etc. (referred to collectively herein asIS-95), are promulgated by the Telecommunication Industry Association(TIA) and other well known standards bodies to specify the use of a CDMAover-the-air interface for cellular or PCS telephony communicationsystems. Exemplary wireless communication systems configuredsubstantially in accordance with the use of the IS-95 standard aredescribed in U.S. Pat. Nos. 5,103,459 and 4,901,307, which are assignedto the assignee of the present invention and fully incorporated hereinby reference.

[0007] A problem arises when a broadcast SMS message is transmitted overthe wireless communication system. The mobile units that are subscribersto the subscription service must acquire the broadcast SMS message in atimely manner, but in order to do so, the mobile units must be awakenedfrom an idle state. The process of “waking up” from the idle state,demodulating the SMS message broadcast from a base station, and thenreturning to the idle state involves a power drain on each mobile unit'sbattery that can measurably diminish the power level of the mobileunit's battery. The length of time in which the mobile unit spends awakeis approximately proportional to the power consumption of the mobileunit.

[0008] Hence, there is a present need to minimize the total batterydrain of the mobile unit while allowing the mobile unit to detect andprocess broadcast SMS messages in a timely manner.

SUMMARY

[0009] The present invention is directed to a method for transmittingand receiving broadcast SMS messages over a broadcast channel in awireless communication system, comprising the steps of: generating aparameter message to be broadcast from a base station to a mobile unit,wherein the parameter message contains a set of transmission parametersfor the broadcast channel; processing the parameter message at themobile unit; and setting a periodic wake up schedule for the mobile unitin accordance with the set of transmission parameters, wherein themobile unit wakes up periodically in order to detect a broadcast SMSmessage in one or more assigned broadcast channel frames. The period foreach category of broadcast SMS messages may be different and the periodmay apply to a single broadcast channel. Messages arriving aperiodicallycan be queued and transmitted in pre-scheduled broadcast channel frames.Messages with inter-arrival interval greater than the specifiedtransmission period are simply repeated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a block diagram of a cellular telephone system.

[0011]FIG. 2 is a block diagram of a processor and associated memoryelements used to generate a transmission parameter message.

[0012]FIG. 3 is a flow chart of one embodiment of the invention.

[0013]FIG. 4 is a timeline of transmission periods for a broadcastchannel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention pertains to a system for transmitting SMSmessages on a broadcast channel. An exemplary wireless communicationsystem in which the present invention is embodied is illustrated inFIG. 1. In a preferred embodiment, the communication system is a CDMAwireless communication system, although it should be understood that thepresent invention is equally applicable to other types of communicationsystems. Systems utilizing other well-known transmission modulationschemes such as TDMA and FDMA as well as other spread spectrum systemsmay employ the present invention.

[0015] As illustrated in FIG. 1, a CDMA wireless telephone systemgenerally includes a plurality of mobile subscriber units 10, aplurality of base stations 12, base station controllers (BSCs) 14, and amobile switching center (MSC) 16. The MSC 16 is configured to interfacewith a conventional public switch telephone network (PSTN) 18. The MSC16 is also configured to interface with the BSCs 14. The BSCs 14 arecoupled to the base stations 12 via backhaul lines. The backhaul linesmay be configured to support any of several known interfaces including,e.g., E1/T1, ATM, IP, PPP, Frame Relay, HDSL, ADSL, or xDSL. It isunderstood that there may be more than two BSCs 14 in the system. Eachbase station 12 advantageously includes at least one sector (not shown),each sector comprising an omnidirectional antenna or an antenna pointedin a particular direction radially away from the base station 12.Alternatively, each sector may comprise two antennas for diversityreception. Each base station 12 may advantageously be designed tosupport a plurality of frequency assignments. The intersection of asector and a frequency assignment may be referred to as a CDMA channel.The base stations 12 may also be known as base station transceiversubsystems (BTSs) 12. Alternatively, “base station” may be used in theindustry to refer collectively to a BSC 14 and one or more BTSs 12. TheBTSs 12 may also be denoted “cell sites” 12. Alternatively, individualsectors of a given BTS 12 may be referred to as cell sites. The mobilesubscriber units 10 are typically cellular or PCS telephones 10. Thesystem is advantageously configured for use in accordance with the IS-95standard.

[0016] During typical operation of the cellular telephone system, thebase stations 12 receive sets of reverse link signals from sets ofmobile units 10. The mobile units 10 are conducting telephone calls orother communications. Each reverse link signal received by a given basestation 12 is processed within that base station 12. The resulting datais forwarded to the BSCs 14. The BSCs 14 provides call resourceallocation and mobility management functionality including theorchestration of soft handoffs between base stations 12. The BSCs 14also routes the received data to the MSC 16, which provides additionalrouting services for interface with the PSTN 18. Similarly, the PSTN 18interfaces with the MSC 16, and the MSC 16 interfaces with the BSCs 14,which in turn control the base stations 12 to transmit sets of forwardlink signals to sets of mobile units 10.

[0017] In accordance with the exemplary wireless communication system,FIG. 2 shows a mechanism 100 for generating a transmission parametermessage including a processor 102, a software module 104, and a storagemedium 106. The processor 102 is advantageously a microprocessor or aspecial-purpose processor such as a digital signal processor (DSP), butmay in the alternative be any conventional form of processor,controller, microcontroller, or state machine. The processor 102 iscoupled to the software module 104, which is advantageously implementedas RAM memory holding software instructions that direct the operation ofthe processor 102. The software instructions can comprise a softwareprogram or a set of microcodes. The RAM memory 104 may be on-board RAM,or the processor 102 and the RAM memory 104 could reside in an ASIC. Inan alternate embodiment, firmware instructions are substituted for thesoftware module 104. The storage medium 106 is coupled to the processor102, and is advantageously implemented as a combination of RAM memoryand any form of conventional nonvolatile memory such as, e.g., ROMmemory. The storage medium 106 is used to store precomputed tables andinstructions. For example, the instructions and tables are stored in theROM memory component while the register is stored in the RAM memorycomponent. In the alternative, the storage medium 106 could beimplemented as either a disk memory or a flash memory that is accessibleby the processor 102. In the alternative, the storage medium 106 may beimplemented as registers. The mechanism 100 may reside in anyconventional communications device such as, e.g., the mobile subscriberunits 10 or the base stations 12 in the CDMA wireless telephone systemof FIG. 1.

[0018]FIG. 3 is a block diagram illustrating an embodiment of theinvention, wherein SMS messages are broadcast periodically oraperiodically from a base station throughout the base station's coveragearea. At step 300, a base station receives subscriber serviceinformation from subscriber services. It should be understood that thebase station may receive information from subscriber services at anytime. At step 310, a mobile unit enters the coverage area of a basestation and acquires system parameters from the base station. Systemparameters include subscriber service transmission parameters thatdefine the wake up schedule for mobile units that have subscribed to asubscription service. At step 320, the mobile unit processes thesubscriber service transmission parameters and sets an internal wake upschedule accordingly. At step 330, the mobile unit begins to follow theinternal wake up schedule, wherein the mobile unit wakes up from an idlestate to periodically scan the broadcast channel for SMS messages. Themethod described herein is repeated each time a mobile unit enters thecoverage area of a new base station. It is understood that all basestations in the wireless communication system will be receiving thesubscriber service information from subscriber services.

[0019] The subscriber service transmission parameter message from thebase station may be transmitted periodically or aperiodically to themobile units that are subscribers to a service in the coverage area. Thesubscriber service transmission parameter message instructs the mobileunits when to wake up from an idle state, demodulate the SMS messagethat may be carried on the broadcast channel, and when to return to anidle state while the mobile units remain in the coverage area of thebase station. Table 1 contains some of the specific parameters that maybe transmitted by the base station. TABLE 1 Parameter Units # of BitsMessage Category N/A 16 Minimum Transmission Period (MTP) 1.28 sec.intervals  8 Transmission Period MTPs  9 or 11 Transmission Offset fromSystem Time BCCH frames Up to 13 in the Minimum Transmission PeriodTransmission Offset from System Time MTPs  9 or 11 in the TransmissionPeriod Number of Repetitions N/A  2 Separation Between Repetitions MTPs 2 Burst Length BCCH frames 10

[0020] System time is the time reference used by the base station and issynchronous to Universal Coordinated Time (UTC), which is aninternationally agreed-upon time maintained by the Bureau Internationalde l'Heure (BIH). Values are assigned to the parameters that correspondto the desired broadcast schedule of each service. The MinimumTransmission Period (MTP) parameter specifies the cycle duration inunits of 1.28 seconds. The numerical value of 1.28 seconds is theminimum slot cycle for mobile stations operating in the slotted modeaccording to IS-95. However, it should be understood that this numericalvalue could be modified without limiting the scope of this invention.

[0021] The Transmission Period Parameter is defined in units of MTP andcan be set so that transmission periods will occur up to a maximum limitof a day (9 bits) or a week (11 bits), according to system parameters.The Transmission Period parameter can be determined from the average ormaximum rate at which new messages arrive. For example, if a SMS messagefrom a subscription service arrives at the base station once every 15minutes, then the Transmission Period for the slot assigned to thatsubscription service should be set to be less than or equal to 15minutes.

[0022] The Transmission Offset from System Time in the MTP parameter isdefined in units of broadcast channel (BCCH) frames and is used toidentify which slot in the MTP is assigned to a specific service. TheTransmission Offset from System Time in the Transmission Periodparameter is defined in units of MTP and is used to identify which slotin the transmission period is assigned to a specific service. TheSeparation Between Repetitions parameter is defined in units of MTP.Repeated transmissions with short separation are used to supportservices that have very long transmission periods. Burst Length isdefined in units of BCCH frames and is used to support messages that arelonger than a broadcast channel frame.

[0023] Using these specific parameters, a base station can choose anarbitrary minimum transmission period that can be divided into slotscorresponding to the broadcast channel frames, which may be 40 ms, 80ms, or 160 ms long or as otherwise defined. The base station cantransmit broadcast SMS messages on the broadcast channel repeatedly,with repetitions of the broadcast SMS message sent in consecutiveframes, or in frames separated by a fixed time interval. Thetransmission schedule that is transmitted from the base station to themobile unit gives the mobile unit the ability to power up for thoseprearranged times when a broadcast SMS message is to be transmitted. Inaddition, the transmission schedule gives the base station flexibilityin structuring the SMS message.

[0024] Using the subscriber service transmission parameters, a mobileunit can scan for specific SMS messages over assigned slots in thebroadcast channel. For example, FIG. 4 is a timeline of exemplarytransmission periods over a broadcast channel, wherein the broadcast SMSmessages are structured flexibly. The length of the broadcast SMSmessage can be a fraction of the length of a broadcast channel frame,the length of a broadcast channel frame, or a multiple of the length ofa broadcast channel frame. The transmission period for service A 410 isequal to the minimum transmission period 401. The transmission period402 for services B 410, C 430, and D 440 is twice the minimumtransmission period 401. The transmission period 403 for services E 450,F 460, G 470, H 480, and I 490 is four times the minimum transmissionperiod 401. Each message for services A 410 through H 480 has theduration of one broadcast channel frame 404 and each message for service1490 spans over two broadcast channel frames.

[0025] For those messages from subscriber services that may not bepreviously scheduled, i.e., emergency news or breaking news stories, thebase station may have a designated service slot that remains emptyduring regular periods, but can be used to carry unscheduled SMSmessages at appropriate times.

[0026] In another embodiment of the invention, the minimum transmissionperiod of the broadcast channel frames can be arbitrarily lengthened toincrease the subscriber service capacity of the wireless communicationsystem. In wireless devices that are broadcast SMS enabled only, i.e.,laptaps, PDAs, pagers, and other data devices, the necessity of constantscans for incoming voice calls is eliminated. In cellular and PCS mobilephones with data capabilities, the service configuration between thebase station and the mobile phone unit include service options for bothvoice and SMS messages (data). Because of the voice service option, theslot cycle for most systems have been set to 1.28 seconds or 2.56seconds, which would allow mobile units to detect the presence ofincoming voice calls in a timely manner. Longer periods increase theprobability that a calling party will disconnect the phone call beforethe mobile unit detects the signal or the mobile unit can notify theuser.

[0027] However, in wireless devices that are not voice-enabled, theconstraint of a short slot cycle is essentially eliminated. The basestation can lengthen the minimum transmission period arbitrarily so thatbroadcast SMS messages can be scheduled for transmission once a week, oronce a day, or once every 1.28 seconds. The alteration of the minimumtransmission period can change the service capabilities of the mobileunit. For example, if all services are transmitted at a rate of onemessage every 32 seconds, and each message lasts for one 160 msbroadcast channel frame, then 200 services can be supported in that 32second period. However, if services are transmitted at a rate of onemessage every 1.28 seconds, and each message lasts for one 160 msbroadcast channel frame, then only 8 services can be supported in the1.28 second period.

[0028] In general, let the minimum transmission period be m×1.28seconds, wherein m is chosen such that 1<m<256 and the broadcast channelframe length be k×40 ms, wherein k=1, 2, or 4. Then there are 32 m/kbroadcast channel frames in each minimum transmission period. If eachmessage is one frame long, then these 32 m/k frames can be used totransmit either:

[0029] 1. a set of 32 m/k messages with the transmission period equal tothe minimum transmission period, or

[0030] 2. a set of 64 m/k services with transmission period twice aslong as the minimum transmission period, or

[0031] 3. a combination of 16 m/k services with transmission periodequal to the minimum transmission period and 32 mA services withtransmission period twice as long as the minimum transmission period.

[0032] Preferred embodiments of the present invention have thus beenshown and described. It would be apparent to one of ordinary skill inthe art, however, that numerous alterations may be made to theembodiments herein disclosed without departing from the spirit of scopeof the invention. Therefore, the present invention is not to be limitedexcept in accordance with the following claims.

I claim:
 1. A method for transmitting and receiving messages over abroadcast channel in a communication system, comprising: generating aparameter message for transmission from a base station to a mobile unit,wherein the parameter message contains a set of transmission parametersfor the broadcast channel; processing the parameter message at themobile unit; setting a periodic wake up schedule for the mobile unit inaccordance with the set of transmission parameters, wherein the mobileunit wakes up periodically in accordance with the periodic wake upschedule in order to detect a broadcast message in one of a plurality ofbroadcast channel frames from at least one of a plurality of subscribermessage services.
 2. The method as recited in claim 1 furthercomprising: determining, for the set of transmission parameters, aminimum transmission period for the mobile unit, wherein the minimumtransmission period is variable; determining, for the set oftransmission parameters, a transmission period, wherein the transmissionperiod has a duration that is a multiple value of the minimumtransmission period, and wherein the transmission period is variable;determining, for the set of transmission parameters, a minimumtransmission period offset, wherein the minimum transmission periodoffset directs the mobile unit to demodulate a specified broadcastchannel frame during the minimum transmission period; determining, forthe set of transmission parameters, a transmission period offset,wherein the transmission period offset directs the mobile unit todemodulate a specified broadcast channel frame during the transmissionperiod,
 3. The method as recited in claim 2 wherein the transmissionperiod has a value greater than or equal to a message arrival rate,wherein the message arrival rate is the rate at which the base stationreceives information from at least one of the plurality of subscribermessage services.
 4. The method of claim 1, wherein at least one of theplurality of broadcast channel frames is reserved for an aperiodicmessaging.
 5. A method for transmitting and receiving messages over abroadcast channel in a communication system, comprising: transmitting aplurality of parameter messages over the broadcast channel, wherein eachof the plurality of parameter messages contains a set of transmissionparameters corresponding to each mobile unit in said communicationsystem or each set of mobile units in said communication system;processing the plurality of parameter messages at each mobile unit;setting a periodic wake up schedule for each mobile unit in accordancewith the corresponding sets of transmission parameters, wherein eachmobile unit wakes up periodically in accordance with the periodic wakeup schedule in order to detect a message in one of a plurality ofbroadcast channel frames from at least one of a plurality of subscribermessage services.
 6. The method as recited in claim 5 furthercomprising: determining, for each of the set of transmission parameters,a minimum transmission period, wherein the minimum transmission periodis variable; determining, for each of the set of transmissionparameters, a transmission period, wherein the transmission period has aduration that is a multiple value of the minimum transmission period,wherein the transmission period has a value greater than or equal to amessage arrival rate, wherein the message arrival rate is the rate atwhich the base station receives information from at least one of theplurality of subscriber message services, and wherein the transmissionperiod is variable; determining, for each of the set of transmissionparameters, a minimum transmission period offset, wherein the minimumtransmission period offset directs each mobile unit to demodulate aspecified broadcast channel frame during the minimum transmissionperiod; determining, for each of the set of transmission parameters, atransmission period offset, wherein the transmission period offsetdirects each mobile unit to demodulate a specified broadcast channelframe during the transmission period from at least one of the pluralityof subscriber message services.
 7. The method of claim 5, wherein atleast one of the plurality of broadcast channel frames is reserved foran aperiodic message.
 8. An apparatus for transmitting and receivingmessages over a broadcast channel in a communication system, comprising:means for generating a parameter message for transmission from a basestation to a mobile unit, wherein the parameter message contains a setof transmission parameters for the broadcast channel; means forprocessing the parameter message at the mobile unit; means for setting aperiodic wake up schedule for the mobile unit in accordance with the setof transmission parameters, wherein the mobile unit wakes upperiodically in accordance with the periodic wake up schedule in orderto detect a broadcast message in one of a plurality of broadcast channelframes from at least one of a plurality of subscriber message services.9. The apparatus as recited in claim 8 further comprising: determining,for the set of transmission parameters, a minimum transmission periodfor the mobile unit, wherein the minimum transmission period isvariable; determining, for the set of transmission parameters, atransmission period, wherein the transmission period has a duration thatis a multiple value of the minimum transmission period, and wherein thetransmission period is variable; determining, for the set oftransmission parameters, a minimum transmission period offset, whereinthe minimum transmission period offset directs the mobile unit todemodulate a specified broadcast channel frame during the minimumtransmission period; determining, for the set of transmissionparameters, a transmission period offset, wherein the transmissionperiod offset directs the mobile unit to demodulate a specifiedbroadcast channel frame during the transmission period,
 10. Theapparatus as recited in claim 9 wherein the transmission period has avalue greater than or equal to a message arrival rate, wherein themessage arrival rate is the rate at which the base station receivesinformation from at least one of the plurality of subscriber messageservices.
 11. The apparatus of claim 8, wherein at least one of theplurality of broadcast channel frames is reserved for an aperiodicmessaging.
 12. An apparatus for transmitting and receiving messages overa broadcast channel in a communication system, comprising: means fortransmitting a plurality of parameter messages over the broadcastchannel, wherein each of the plurality of parameter messages contains aset of transmission parameters corresponding to each mobile unit in saidcommunication system or each set of mobile units in said communicationsystem; means for processing the plurality of parameter messages at eachmobile unit; means for setting a periodic wake up schedule for eachmobile unit in accordance with the corresponding sets of transmissionparameters, wherein each mobile unit wakes up periodically in accordancewith the periodic wake up schedule in order to detect a message in oneof a plurality of broadcast channel frames from at least one of aplurality of subscriber message services.
 13. The apparatus as recitedin claim 12 further comprising: means for determining, for each of theset of transmission parameters, a minimum transmission period, whereinthe minimum transmission period is variable; means for determining, foreach of the set of transmission parameters, a transmission period,wherein the transmission period has a duration that is a multiple valueof the minimum transmission period, wherein the transmission period hasa value greater than or equal to a message arrival rate, wherein themessage arrival rate is the rate at which the base station receivesinformation from at least one of the plurality of subscriber messageservices, and wherein the transmission period is variable; means fordetermining, for each of the set of transmission parameters, a minimumtransmission period offset, wherein the minimum transmission periodoffset directs each mobile unit to demodulate a specified broadcastchannel frame during the minimum transmission period; determining, foreach of the set of transmission parameters, a transmission periodoffset, wherein the transmission period offset directs each mobile unitto demodulate a specified broadcast channel frame during thetransmission period from at least one of the plurality of subscribermessage services.
 14. The apparatus of claim 12, wherein at least one ofthe plurality of broadcast channel frames is reserved for an aperiodicmessage.